Open Source :SPTWebMail

SPTWebMail is a web mail application with AJAX support that uses JavaMail.
Available at: https://sptwebmail.dev.java.net/

Open Source: send-only SMTP server

Aspirin is an embeddable send-only SMTP server that reuses parts of the Apache James mail server.
Available at: https://aspirin.dev.java.net/

Open Source :Mobile Agent 2.0

Allows users with any mobile email enabled device to access their files, open attachments, and forward mail on the go.
GPL License  at: http://www.phenomenatech.com

Open Source :Coadunation is a platform independent server implemented in Java

The latest version includes an Email Server, Web Mail Frontend, DNS Server, and Web Administration Console. Coadunation is an Open Source project provided under the GPL license and is available at: http://www.coadunation.net/

Open Source : JavaMail API

Jack Mail Client is a simple mail client that uses any mail server with minimal configuration. Jack Mail Client is written in pure Java and is available under the GPL license at: http://sourceforge.net/projects/jackmailclient

Open Source : Facebook API client implemented in Java

Google cod you can find open source code  Facebook API client implemented in Java

A Facebook API client implemented in Java, derived from the poorly-maintained official Facebook client.

Download and view got to http://code.google.com/p/facebook-java-api/